The serratus anterior is a muscle of your shoulder girdle that is situated in front of your torso. This muscle connects the underside of the middle border of your scapula to the front of your rib cage. Due to this orientation, when it contracts and shortens, the serratus anterior causes your scapula to move forward and tilt to the side. It also acts in conjunction with your trapezius to rotate your scapula upward, which is necessary when you move your arm.
Movements
The serratus anterior is important for reaching and pushing because these actions require the scapula to be drawn toward the ribs. Its contribution to upward rotation of the scapula is also critical because every time you raise your arm to the front or side, your shoulder joint must reposition so that the head of your upper arm bone maintains its place in the scapula's socket. This socket is very shallow, so if repositioning did not occur, you wouldn't be able to raise your arm without dislocating the joint. Accordingly, individuals with a paralyzed serratus anterior cannot elevate their arm above 100 degrees.
Posture
If your serratus anterior is weak, your shoulder blade might protrude from the surface of your back. This postural abnormality is known as a winged scapula. The protrusion is particularly apparent along the scapula's medial border and will be clearly visible when you are performing a push up. A tight serratus anterior can also create postural deviations. For example, at rest, the medial border of your scapula should be positioned approximately two inches from your spine. If your serratus anterior is not long enough to allow for this orientation, your scapula will be pulled forward, which contributes to a round-shouldered stature.
Exercise
To strengthen the serratus anterior in an isolated manner, you must perform a resistance-training movement that involves motion of the shoulder girdle exclusively. This means that your arm should not move at the shoulder and your elbow should remain straight as you contract the muscle. One alternative is to lie supine on a bench with a dumbbell in each hand and your arms extended fully over your chest such that the angle formed by your upper arm in relation to your torso is 90 degrees. If you are experienced with resistance training, you will recognize this as the finishing point of a bench press. From this position, you should push the dumbbells upward by moving your shoulder blades forward. You will only be able to cover a short range of motion when doing this, so don't expect to be moving very far. Once your shoulder blades are drawn forward, you should hold the contracted position momentarily before slowly lowering to the starting position and repeating for the desired number of repetitions.
ACSM Guidelines
The American College of Sports Medicine has published recommendations for weight training that can be used to determine the optimal volume, frequency and intensity for training your serratus anterior. These guidelines indicate that it is sufficient to perform one set of eight to 12 repetitions to volitional fatigue per muscle each session in order to bring most of the improvement in strength because more sets will only elicit slightly greater gains. They also suggest that two training sessions per week should suffice. However, exercises must be performed through a full range of motion and proper technique should be strictly maintained. Collectively, these mandates indicate that it is quality and not quantity that is the important factor when strengthening your muscles.
References
- "ACE Personal Trainer Manual 4th Edition"; American Council on Exercise; 2010
- "Kinesiology: Scientific Basis of Human Motion Twelfth Edition"; N. Hamilton, W. Weimar and K. Luttgens 2008
- ExRx.net: Weight Training Guidelines
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